In recent years, rapidly improving performance of the mobile devices and the convergence of the components of various functions and performances have necessitated cooperation between appropriate interfaces. MIPI is an abbreviation of “Mobile Industry Processor Interface” and was established to define the interface between respective components that constitute a mobile device.
In MIPI, a serial method is mainly used for interfacing between the internal devices of the mobile device. In order to simplify the hardware configuration using a serial method and to enable a high-speed interface, a differential pair method is used. There are two types of serial interface of this differential pair type used in MIPI, which are: D-PHY and M-PHY. D-PHY is mainly used for cameras or LCD displays, and M-PHY is used for a higher-speed interface such as WiFi.
FIG. 1 is a diagram provided to explain a signal mode in the MIPI D-PHY, and FIG. 2 is a diagram illustrating an Analog-PHY block of the MIPI D-PHY.
As illustrated in FIG. 1, in the MIPI D-PHY specification, one single physical line is used with a combination of two modes of LP (Low Power) mode and HS (High Speed data) mode, and a signal is transmitted while mode changes.
In the MIPI D-PHY specification, LP (Low Power) section and HS (High Speed data) section are precisely divided, and in the MIPI D-PHY, the signals that would otherwise be mixed in the MIPI D-PHY are separated into an LP signal and an HS signal, respectively, as shown in FIG. 2.
However, there is a problem that, as the MIPI transmission rate increases, the clocks and the transmission delay of each data signal line are not constant for each of the signals depending on the environment such as line length, impedance matching, and so on at the transmission end. Therefore, there is a problem of receiving incorrect data when receiving MIPI data at the receiving end.
In the MIPI D-PHY specification, the LP signals are slow section where no skew compensation would be necessary, such that the starting and ending of the packet data transmitted in the HS section can be accurately checked according to the state of the LP signals. On the other hand, the HS section in which the actual packet data is transmitted is where high-speed packet data is transmitted, and accordingly, presence of a skew difference between the clock signal and each data signal will make reception of normal packet data impossible. Accordingly, a skew correction is indispensable.
Generally, the MIPI D-PHY reception system employs a method of manually compensating the skew of each signal at the transmitting end or the receiving end in order to compensate the skew between the data signal and the clock signal.
In order to solve this skew problem in high-speed transmission, a MIPI system after the MIPI D-PHY 1.2 specification is added with a function, in which pattern data for deskew purpose is included in each of the MIPI packets at the transmitting end so that the receiving end receiving the corresponding pattern data automatically compensates the skew in real time with the evaluation process.
However, for a MIPI system that does not support the deskew function of the MIPI D-PHY 1.2, skew cannot be compensated or has to be compensated manually which can be inconvenient. On the other hand, a method of adjusting and compensating the skew at the transmitting end, and a method of manually adjusting the clock signal or the skew of the data signal every time at the receiving end also have shortcomings, because a possible abnormality in the received data has to be checked with the process of adjusting one step at a time according to the number of skew steps defined according to each transmitting end, which takes a considerable amount of time until normal data is received.